Measuring low resistance – which is usually taken to mean resistance of less than 1Ω – has many applications, from checking the condition of circuit breaker contacts to verifying the integrity of welds in metal structures. One very common question however is, “What’s the best test current to use?” As is usual with questions like this, there is no simple “one size fits all” answer.

Megger regularly collaborates with vendor-neutral training centers to provide the most experienced instructors so that students receive the best classroom learning experience. Read more about Megger’s instructor Marshal Bird at the Mesa Hotline School.

When a breaker fails to open contacts or interrupt current after receiving a tripping signal from a primary relay, we have a breaker failure. Most protection systems have a breaker-failure scheme and it is important to test this backup protection as part of your regular relay testing program.

Ground faults often develop in substation battery systems over time due to environmental factors and maintenance activities. Dirt and debris accumulated on battery surfaces can create electrical paths to the battery rack. Electrolyte residue due to cracking or crazing of the battery container also results in conduction paths to the battery rack. This application note will cover how to use the Megger BGL to trace and locate ground faults on a live DC system, without sectionalizing any circuits.